全文获取类型
收费全文 | 1368篇 |
免费 | 88篇 |
国内免费 | 24篇 |
出版年
2023年 | 26篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 39篇 |
2019年 | 73篇 |
2018年 | 52篇 |
2017年 | 36篇 |
2016年 | 36篇 |
2015年 | 41篇 |
2014年 | 95篇 |
2013年 | 62篇 |
2012年 | 62篇 |
2011年 | 70篇 |
2010年 | 55篇 |
2009年 | 60篇 |
2008年 | 79篇 |
2007年 | 77篇 |
2006年 | 51篇 |
2005年 | 56篇 |
2004年 | 39篇 |
2003年 | 30篇 |
2002年 | 35篇 |
2001年 | 19篇 |
2000年 | 31篇 |
1999年 | 29篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1971年 | 2篇 |
排序方式: 共有1480条查询结果,搜索用时 15 毫秒
1.
Roland Sturm 《Biometrical journal. Biometrische Zeitschrift》1991,33(4):441-454
This paper discusses discrete time proportional hazard models and suggests a new class of flexible hazard functions. Explicitly modeling the discreteness of data is important since standard continuous models are biased; allowing for flexibility in the hazard estimation is desirable since strong parametric restrictions are likely to be similarly misleading. Simulation compare continuous and discrete models when data are generated by grouping and demonstrate that simple approximations recover underlying hazards well and outperform nonparametric maximum likelihood estimates in term of mean squared error. 相似文献
2.
Takatoshi Murata Tsutomu Sato Takeshi Kamoda Hiromitsu Moriyama Yasuo Kumazawa Nobuhiro Hanada 《Experimental cell research》2014
Hydrogen sulfide (H2S) is a novel gasotransmitter that plays multiple biological roles in various body systems. In addition to its endogenous production, H2S is produced by bacteria colonizing digestive organs, including the oral cavity. H2S was previously shown to enhance pro-apoptotic effects in cancer cell lines, although the mechanisms involved remain unclear. To properly assess the anti-cancer effects of H2S, however, investigations of apoptotic effects in normal cells are also necessary. The aims of this study were (1) to compare the susceptibility to H2S-induced apoptosis between the oral cancer cell line Ca9-22 and oral keratinocytes that were derived from healthy gingiva, and (2) to identify candidate genes involved in the induction of apoptosis by H2S. The susceptibility to H2S-induced apoptosis in Ca9-22 cells was significantly higher than that in keratinocytes. H2S exposure in Ca9-22 cells, but not keratinocytes, enhanced the expression of pleckstrin homology-like domain, family A, member 1 (PHLDA1), which was identified through a differential display method. In addition, PHLDA1 expression increased during actinomycin D-induced apoptosis in Ca9-22 cells. Knockdown of PHLDA1 expression by small interfering RNA in Ca9-22 cells led to expression of active caspase 3, thus indicating apoptosis induction. The tongue cancer cell line SCC-25, which expresses PHLDA1 at a high level, showed similar effects. Our data indicate that H2S is an anti-cancer compound that may contribute to the low incidence of oral cancer. Furthermore, we demonstrated the role of PHLDA1 as an apoptosis suppressor. 相似文献
3.
4.
5.
On blocking rules for the bootstrap with dependent data 总被引:9,自引:0,他引:9
We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton1/3, n1/4 and n1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically. 相似文献
6.
Abstract. Plant cover was visually estimated by five observers, independent of each other, in a species‐rich grassland in the Bílé Karpaty Mts., southeastern Czech Republic, in seven plots ranging from 0.001 to 4 m2. Variation of total plant cover among the observers was high at small scales: 0.001–0.016 m2; coefficient of variation, CV = 35 to 45%, but much lower at larger scales: 0.06–4 m2; CV = 7 to 15%. Differences between visual estimates of plant cover of individual species made by different observers were affected by plot size, total cover and morphology of particular plants. CV of the cover of individual species ranged from 0 to 225% and decreased with increasing plot size. For abundant plants the CV attained ca. 50%, independent of plot size. In spite of a very high number of sterile plants with similar leaf morphology and colour, the observed variation in cover estimates in the studied grassland was comparable with results reported from other vegetation types. Differences between estimates by individual observers were often larger than usual year to year changes in undisturbed grasslands. Therefore, I suggest that to avoid difficulties in the interpretation of results based on plant cover data obtained from visual estimates, several observers should always work together, adjusting their extreme estimates. 相似文献
7.
8.
Parvinder Kaur 《Biometrical journal. Biometrische Zeitschrift》1985,27(1):107-110
For the estimation of population mean in simple random sampling, an efficient regression-type estimator is proposed which is more efficient than the conventional regression estimator and hence than mean per unit estimator, ratio and product estimators and many other estimators proposed by various authors. Some numerical examples are included for illustration. 相似文献
9.
Biosorption potential of Azolla microphylla for acid red 88 from aqueous solution was investigated under laboratory conditions as a function of initial pH and temperature. The algal biomass exhibited the highest dye sorption capacity at optimum conditions of pH 3 and temperature 30°C. The experimental isotherms were analyzed using five two-parameter models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Flory-Huggins) and five three-parameter models (Redlich-Peterson, Sips, Khan, Radke-Prausnitz, and Toth). Three error analysis methods were used to evaluate the experimental data: correlation coefficient, residual root mean square error (RMSE), and chi-square test to find the best fitting isotherm. In particular, Langmuir (two-parameter) and Khan (three-parameter) models described the dye biosorption isotherm data well at all pH and temperature conditions examined. 相似文献
10.